As a shell material of a capsule used for foods, pharmaceuticals, quasi-drugs and the like, a gelatin has been mainly used in view of rapid disintegrability in the body, high shell strength and stable moisture absorbing/releasing properties.
However, since gelatin is animal protein from livestock, such as cow, swine, poultry and the like, it is difficult to contain a substance that reacts with a protein as a capsule content therein. It is problem that the gelatin shell is easily insoluble or brittle with time and the heat resistance thereof is degraded when the moisture is increased. There have been cases that gelatin is incepted to have an allergy thereto and is restricted to use religiously or from vegetarism. In addition, recently, it has been difficult to use gelatin for the reason of infection or contamination of livestock diseases, such as mad cow disease (BSE), foot and mouth disease to human.
Therefore, it has been required to develop non-gelatinous capsule shell without using gelatin as a base.
Examples of the non-gelatinous capsule shells include a capsule shell containing water-insoluble agar as a base (for example, described in Japanese Patent Kokai Publication Nos. 193216/1989, 65222/1993, 196478/1995, 25228/1997, 253112/1999 and the like). However, when applying the capsule shell to foods, quasi-drugs and pharmaceuticals, it is difficult to rapidly release them in the body because of bad disintegrability thereof in the body.
A capsule shell containing carrageenan, polysaccharides and polyhydric alcohols as a base (described in Japanese Patent Kokai Publication No. 10508/1986) and a capsule shell obtained by gelling water-soluble base, such as hydroxypropylmethylcellulose, gellan gum or polyvinyl alcohol, by a gelling agent, such as carrageenan (described in Japanese Patent Kokai Publication Nos. 208458/1996, 291928/1998, 170137/2001 and the like), are disclosed. In these capsule shells, since high strength gel is formed by the base, the capsule strength is high, but the disintegration of the capsule shell is difficult, and the rapid disintegrability in the body is not sufficiently obtained. On the other hand, when using a base to low strength gel, the disintegration of the capsule shell is improved, but the capsule strength is low, and it is difficult to produce a capsule product. In addition, the capsule shell is broken after producing, and the capsule content leaks.
In U.S. Pat. No. 6,214,376, a capsule shell containing carrageenan and starch hydrolyzate, such as dextrin having a DE of not less than 10 is disclosed. However, the capsule is brittle and the moisture absorbing/releasing properties are increased, which causes the cracking or softening and stickiness of the capsule shell, and the storage stability is degraded.
As described above, in the conventional well-known technique, it has been difficult to provide a capsule shell that both the strength and easy disintegrability of the capsule shell, which are contrary to each other, can be accomplished and the quality can be retained by stabilizing the moisture absorbing/releasing properties.